CHAPTER ONE INTRODUCTION
1.1 BACKGROUND OF STUDY
1.1.1 CORROSION
Corrosion is defined as a natural process, which converts refined metal to their more stable oxide. It is the gradual destruction or degradation of materials (usually metals) by chemical reaction with their environment which are most likely inevitable. Corrosion is a natural and costly process of destruction like earthquakes, tornados, floods and vocanic eruptions, with one major difference. Whereas we can be only a silent spectator to the above processes of destruction, corrosion can be prevented or at least be controlled.
Despite different definitions, it can be observed that corrosion is basically the result of interaction between materials and their environment. Up to the 1960’s, the term corrosion was restricted only to the metals and their alloys and it did not incorporate ceramics, polymers, composites and semiconductors in its regime. The term corrosion now encompasses all types of natural and man – made materials including biomaterials and nanomaterials, and it is not confined to metals and alloys alone. The scope of corrosion is consistent with the revolutionary changes in materials development witnessed in recent years.
1.1.1.2 CORROSION AND ITS MECHANISM
In nature, metals are not found in free state due to their reactivity. Metals are generally in high energy state because some energy is added during their manufacturing process from the ores. Low energy – state ores are more stable than the high energy – state metals. As a result of this uphill thermodynamic struggle, the metals have a strong driving force to release energy and go back to their original form. Hence the metals revert to their parent state or ore under a suitable corrosive environment. The electrochemical process involved in corrosion by nature is opposite to the extractive metallurgy involved in manufacturing of the metals.
According to electrochemistry, the corrosion reaction can be considered as taking place by two simultaneous reactions:
The oxidation of a metal at an anode (a corroded end releasing electrons) and the reduction of a substance at a cathode (a protected end receiving electrons). In order for the reaction to occur, the following conditions must exist:
1. Two areas on the structure must differ in electrical potential.
2. Those areas called anodes and cathodes must be electrically interconnected.
3. Those areas must be exposed to a common electrolyte.
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THE INHIBITIVE EFFECT OF ALANINE ON CORROSION OF ALUMINIUM IN 0.5 M HCL SOLUTION USING THE WEIGHT LOSS TECHNIQUE
